Preoperative saphenous venography was performed in 100 extremities in 60 patients to evaluate the saphenous vein for use as an arterial bypass graft. In 18 of the patients (30%), venography demonstrated vein abnormality, disease, or small size, which significantly influenced the management of the patient or the conduct of the operation. Good correlation was observed between venographically determined saphenous vein anatomy and diameter and those observed at operation in 52 patients. The average diameter of the saphenous veins on preoperative venograms was 3.4 mm (range, 1.0 to 6.0 mm). These veins dilated to an average diameter 73 +/- 5% greater than that observed venographically, so that the average diameter of harvested, dilated saphenous veins was 5.5 mm (range, 3.0 to 10.0 mm). All veins measuring 2.0 mm or more on the venograms dilated to 4.0 mm or more at operation and were suitable for femoropopliteal or small vessel bypass grafts. Four saphenous veins measuring 1.0 mm or more on the venograms dilated to 3.0 mm or more at operation and were suitable for small vessel bypasses. Thus preoperative saphenous venography can be of value in lower extremity arterial reconstructions. The procedure allows detection of anomalies and disease processes that would prevent the use of one or both saphenous veins as arterial bypass grafts and identifies the best available venous segment thereby obviating unnecessary incisions and minimizing operating time.